scholarly journals On the variability of squeezing behaviour in tunnelling

2020 ◽  
Author(s):  
Florence Mezger
Keyword(s):  
Rock Mass ◽  
Numerical Modelling ◽  
Large Scale ◽  
Tunnel Construction ◽  
Squeezing Ground ◽  
Rock Structure ◽  
Temporary Support ◽  
Remedial Actions ◽  
Additional Costs ◽  
Project Engineer

The magnitude of squeezing deformations in tunnelling often varies over short distances, even if there is no obvious change in the construction method, in the depth of cover, in the lithology or rock structure. As long as the reasons for the variability are not known, the tunnelling-induced convergences cannot be predicted with sufficient reliability. Reliable predictions, however, are important for determining the temporary support or the excavation diameter. Otherwise, large-scale tunnel repairs may be necessary, which can cause delay and additional costs due to remedial actions as well as due to the enforced interruption of other operations in progress at the same time. The analysis of different case studies concerning the AlpTransit project shows that the squeezing variability can be traced back to the heterogeneities in the rock mass at different scales as well as the variation of the orientation of the planes of anisotropy (bedding or schistosity) to the tunnel axis. In order to improve safety and economy of tunnel construction in squeezing ground, the influence of these factors on the convergences was determined quantitatively (by means of analytical solutions or numerical modelling), so that they can be used as indicators during construction for the timely identification and prediction of the squeezing behaviour. Particular attention was paid on factors, whose variation, even if small, may affect the convergences sensitively . Based on these quantitative investigations, design aids were developed, which should help the project engineer to estimate and better understand the variability of the squeezing intensity. The squeezing variability also concerns TBM tunnelling: In contrast to conventional tunnelling, shielded TBMs are particularly vulnerable to squeezing due to the very limited space available. Therefore, in order to better deal with the squeezing variability in TBM tunnelling, different (stiff as well as deformable) lining options were discussed.

Instability in Himalayan Rock Slope under Recurrent Freeze-Thaw

2020 ◽  
Author(s):  
Sahil Sardana ◽  
Rabindra Kumar Sinha ◽  
Mamta Jaswal ◽  
Amit Kumar Verma ◽  
Trilok Nath Singh
Keyword(s):  
Rock Mass ◽  
Numerical Modelling ◽  
Rock Slope ◽  
Winter Season ◽  
Intact Rock ◽  
Joint Spacing ◽  
Freeze Thaw ◽  
Discontinuity Sets ◽  
Rock Structure ◽  
The Stability

<p>The highways in the Himalayas region have an important concern as these are the only connecting corridors to the nearby land area. Manali-Leh highway is one such important route in India which is interrupted frequently by landslides and rockslides events due to freeze-thaw activity, earthquake, heavy rainfall and anthropogenic activities are major triggering factors. In the freeze-thaw activity, water enters into the cracks in rocks during rainfall, subsequently, it freezes, leads to enlargement of cracks and/or the initiation of new cracks due to the volumetric expansion of ice. In the summer season, the ice melts and water migrates to the newly generated cracks and later freezes in the winter season. This, in turn, weakens the rock structure that leads to the reduction of the rock mass strength which promotes instability in the rock slopes. This study focuses on the stability assessment of rock slope along the highway from Solang Valley in Himachal Pradesh, India. This highway connects the Solang Valley to the south portal of the Rohtang tunnel and provides all-weather connectivity, as the Manali-Leh highway shut down during the winter season due to heavy snowfall.</p><p>An extensive geotechnical survey was carried out on the studied slope and the rock samples were collected from the field. The artificial freeze-thaw environment was created in the laboratory for the rock specimens to account the natural freeze-thaw effect. Laboratory tests were conducted on the rock specimen conditioned with freeze-thaw to determine the physico-mechanical parameters of intact rock prior to the numerical simulation. The results indicate the significant loss in compressive and tensile strength of rock as the number of freeze-thaw cycles increases. A three-dimensional numerical modelling was performed to assess the stability of the rock slope using the Distinct Element Code (3DEC software). Slope geometry was prepared to represent the actual slope and the various discontinuity sets observed at the field was mapped on the model. The behaviour of the discontinuity sets was modelled using a Mohr-Coulomb slip with residual strength. Normal stiffness of the joints was calculated from rock mass deformation modulus, intact rock young’s modulus and joint spacing. Similarly, the shear stiffness was calculated. The results of numerical modelling show that the displacement of blocks increases and the factor of safety of the slope decreases as the number of freeze-thaw cycles increases.</p>

In Situ Tests on Creep Behavior of Rock Mass with Joint or Shearing Zone in Foundation of Large-Scale Hydroelectric Projects

2004 ◽  
Vol 261-263 ◽  
pp. 1097-1102 ◽  
Author(s):  
Jian Liu ◽  
Xia Ting Feng ◽  
Xiu Li Ding ◽  
Huo Ming Zhou
Keyword(s):  
Rock Mass ◽  
Creep Behavior ◽  
Large Scale ◽  
Time Dependent ◽  
Three Gorges Project ◽  
Three Gorges ◽  
The Three Gorges ◽  
The Three Gorges Project

The time-dependent behavior of rock mass, which is generally governed by joints and shearing zones, is of great significance for engineering design and prediction of long-term deformation and stability. In situ creep test is a more effective method than laboratory test in characterizing the creep behavior of rock mass with joint or shearing zone due to the complexity of field conditions. A series of in situ creep tests on granite with joint at the shiplock area of the Three-Gorges Project and basalt with shearing zone at the right abutment of the Xiluodu Project were performed in this study. Based on the test results, the stress-displacement-time responses of the joints and basalt are analyzed, and their time-dependent constitutive model and model coefficients are given, which is crucial for the design to prevent the creep deformations of rock masses from causing the failure of the operation of the shiplock gate at the Three-Gorges Project and long-term stability of the Xiluodu arc dam.

Study on Deformation and Damage of Rock Mass Subject to High In Situ Stress by Using a Elastoplastic Damage Model and Considering the Impact of Weak Planes

2013 ◽  
Vol 838-841 ◽  
pp. 705-709
Author(s):  
Yun Hao Yang ◽  
Ren Kun Wang
Keyword(s):  
Rock Mass ◽  
Large Scale ◽  
Damage Model ◽  
Back Analysis ◽  
In Situ Stress ◽  
Surrounding Rock ◽  
High In Situ Stress ◽  
Underground Caverns ◽  
The Impact

Large scale underground caverns are under construction in high in-situ stress field at Houziyan hydropower station. To investigate deformation and damage of surrounding rock mass, a elastoplastic orthotropic damage model capable of describing induced orthotropic damage and post-peak behavior of hard rock is used, together with a effective approach accounting for the presence of weak planes. Then a displacement based back analysis was conducted by using the measured deformation data from extensometers. The computed displacements are in good agreement with the measured ones at most of measurement points, which confirm the validities of constitutive model and numerical simulation model. The result of simulation shows that damage of surrounding rock mass is mainly dominated by the high in-situ stress rather than the weak planes and heavy damage occur at the cavern shoulders and side walls.

scholarly journals Using plants to remediate or manage metal-polluted soils: an overview on the current state of phytotechnologies

2021 ◽  
Vol 43 ◽  
pp. e58283
Author(s):  
Clístenes Williams Araújo do Nascimento ◽  
Caroline Miranda Biondi ◽  
Fernando Bruno Vieira da Silva ◽  
Luiz Henrique Vieira Lima
Keyword(s):  
Large Scale ◽  
State Of The Art ◽  
Cost Effective ◽  
Time Frame ◽  
Contaminated Site ◽  
Polluted Soils ◽  
Mining Sites ◽  
Current State ◽  
Remedial Actions ◽  
The Tropics

Soil contamination by metals threatens both the environment and human health and hence requires remedial actions. The conventional approach of removing polluted soils and replacing them with clean soils (excavation) is very costly for low-value sites and not feasible on a large scale. In this scenario, phytoremediation emerged as a promising cost-effective and environmentally-friendly technology to render metals less bioavailable (phytostabilization) or clean up metal-polluted soils (phytoextraction). Phytostabilization has demonstrable successes in mining sites and brownfields. On the other hand, phytoextraction still has few examples of successful applications. Either by using hyperaccumulating plants or high biomass plants induced to accumulate metals through chelator addition to the soil, major phytoextraction bottlenecks remain, mainly the extended time frame to remediation and lack of revenue from the land during the process. Due to these drawbacks, phytomanagement has been proposed to provide economic, environmental, and social benefits until the contaminated site returns to productive usage. Here, we review the evolution, promises, and limitations of these phytotechnologies. Despite the lack of commercial phytoextraction operations, there have been significant advances in understanding phytotechnologies' main constraints. Further investigation on new plant species, especially in the tropics, and soil amendments can potentially provide the basis to transform phytoextraction into an operational metal clean-up technology in the future. However, at the current state of the art, phytotechnology is moving the focus from remediation technologies to pollution attenuation and palliative cares.

Optimizing Method of Main Caverns in Large Underground Water-Sealed Storage Caverns

2021 ◽  
Author(s):  
Yang An ◽  
E-chuan Yan ◽  
Xing-ming Li ◽  
Shao-ping Huang
Keyword(s):  
Rock Mass ◽  
Large Scale ◽  
Distinct Element ◽  
Strength Criterion ◽  
Axial Direction ◽  
Optimization Method ◽  
Underground Water ◽  
Land Resource ◽  
Maximum Displacement ◽  
Distinct Element Code

Abstract As a main method of petroleum strategic reserve in China, underground water-sealed storage cavern owns lots of outstanding advantages, such as low operating costs, high safety, and land resource conservation. Main caverns are important structure in underground project and the layout parameters and excavation scheme will have significant impact on overall project quality. The optimization method of main cavern layout and excavation scheme was put forward by a proposed large-scale underground water-sealed cavern project in China. First, based on field survey results, the Hoek-Brown strength criterion combined with rock mass quality Q classification system was used to estimate the equivalent mechanical parameters of rock mass. Second, the numerical experiments were carried out by relying on 3 Dimensions Distinct Element Code (3DEC). The discontinuous medium model was adopted, and displacements of key points, maximum displacement values and volume of the plastic zone were used as evaluation indicators. Axial direction, buried depth, spacing and excavation scheme of main caverns have been optimized. Results showed that axial direction should adopt NW325°, buried depth of cavern roof should locate at -100m, and distance between adjacent main caverns should be 1.5 times the span (36m). The “jump excavation” mode was recommended in construction. That is, the caverns on both sides should be excavated first, and the middle cavern should be excavated later. This mode could effectively reduce the interaction effect between caverns. This method has the characteristics of easy data acquisition and strong operability. It could be used to guide design and construction of similar projects . As a main method of petroleum strategic reserve in China, underground water-sealed storage cavern owns lots of outstanding advantages, such as low operating costs, high safety, and land resource conservation. Main caverns are important structure in underground project and the layout parameters and excavation scheme will have significant impact on overall project quality. The optimization method of main cavern layout and excavation scheme was put forward by a proposed large-scale underground water-sealed cavern project in China. First, based on field survey results, the Hoek-Brown strength criterion combined with rock mass quality Q classification system was used to estimate the equivalent mechanical parameters of rock mass. Second, the numerical experiments were carried out by relying on 3 Dimensions Distinct Element Code (3DEC). The discontinuous medium model was adopted, and displacements of key points, maximum displacement values and volume of the plastic zone were used as evaluation indicators. Axial direction, buried depth, spacing and excavation scheme of main caverns have been optimized. Results showed that axial direction should adopt NW325°, buried depth of cavern roof should locate at -100m, and distance between adjacent main caverns should be 1.5 times the span (36m). The “jump excavation” mode was recommended in construction. That is, the caverns on both sides should be excavated first, and the middle cavern should be excavated later. This mode could effectively reduce the interaction effect between caverns. This method has the characteristics of easy data acquisition and strong operability. It could be used to guide design and construction of similar projects .

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